Ultrasonic Transducer and Ultrasonic Flow Measuring Device

ABSTRACT

Ultrasonic transducer (1) comprising a coupling element (3) and a piezo element (2), wherein a metal disk (4) is arranged between the coupling element (3) and the piezo element (2), wherein the metal disk (4) is connected with the piezo element (2) or with the coupling element (3) by means of an adhesive layer (5 or 6), characterized in that the adhesive layer (5 or 6) is producible, at least in certain regions, by means of a photochemically curable adhesive.

TECHNICAL FIELD

The present invention relates to an ultrasonic transducer and to anultrasonic, flow measuring device.

BACKGROUND DISCUSSION

A large number of different variants and layer sequences of ultrasonictransducer structures are already known.

European Patent, EP 0 974 814 B1 of the field of the invention describesa coupling element having a bearing surface, respectively contactsurface. The coupling element has a cavity for accommodating a piezoelement. Arranged between the coupling element and the piezo element isa metal disk. This metal disk is adhered in a plane inclined to thebearing surface and forming a base of the cavity. This construction withintegrated metal disk has basically proved itself and is distinguishedin comparison to glass- and ceramic disks through its high loadabilityin the face of variable temperature loading.

In the manufacture of a plurality of layers, such as in EP 0 974 814 B1,attention is to be given that the elements are oriented relative to oneanother as accurately as possible. Thus, e.g. the metal disk should beoriented as parallel as possible to the ultrasonic transducer. In suchcase, an adhesive can be utilized. During the curing of the adhesive, ashifting of the individual components can be experienced e.g. due totransport related shaking or for other reasons.

It is, consequently, of interest to achieve an as fast as possiblefixing of the individual components in place. A faster curing of theadhesive e.g. by overdosing of hardener or an increased temperatureregimen can, however, lead to stress cracks or otherwise negativelyaffect the properties of the coupling element or lead to disadvantageouseffects (among others, air bubbles) within the adhesive layers. In thesecases, the ultrasonic transducer is lacking in quality.

German Patent, DE 10 2012 207 871 A1 discloses the application of aphotochemically curable adhesive for affixing an intermediate layer. Inthis publication, it is, however, explicitly required that theintermediate layer to be affixed should be at least partiallytransparent. In such case, primarily a full surface curing of theadhesive is assumed, so that, as much as possible, a full surfaceirradiation is provided. A metal disk, as a heat conduction capable,intermediate layer, as is provided in EP 0 974 814 B1, consequently goesagainst the concept of DE 10 2012 207 871 A1, since it is nottransparent.

Moreover, in German Patent, DE 10 2013 104 542 A1, an ultrasonictransducer element with a coupling layer is described, in which likewisea metal disk is applied.

It is an object of the present invention to provide an ultrasonictransducer, which is rapidly producible and, in given cases, with leastpossible temperature loading.

The invention achieves this object by an ultrasonic transducer includinga coupling element and a piezo element, wherein between the couplingelement and the piezo element a metal disk is arranged. The metal diskis connected with the piezo element by means of an adhesive layer.

The metal disk is provided to be covered by the piezo element and can bearranged in a cavity of the coupling body. Additionally, this metal diskcan also be provided with an additional layer of a non-metallicmaterial.

Ideally, the metal disk has a preferred layer thickness of less than ⅛ λ(lambda), preferably less than 1/16 λ. It does not perform the functionof an acoustic matching, but, instead, only provides thermal adjustmentbetween the piezo element and layers arranged therebeneath—respectivelythe coupling element and, in given cases, an adapting, or matching,layer. The metal disk has, in such case, preferably a thermalcoefficient of expansion of less than 30 ppm/K, especially preferablyless than 25 ppm/K. The metal disk should be as flat as possible, inorder that it lead to no angular displacement between the plane of thebase of the coupling element relative to the plane of the piezo element.The flatness of the metal disk amounts, in such case, preferably, toless than 1/16, especially less than 1/32 lambda.

In a first variant of the invention, the adhesive layer is at least incertain regions producible by means of a photochemically curableadhesive.

In a second variant of the invention, the adhesive layer is at least incertain regions producible from an adhesive, which contains at least onemicro-encapsulated polymerization activating component, which isreleasable under the action of ultrasonic waves.

The curing can, in such case, be introduced by the in any event presentpiezo element of the ultrasonic transducer. Thus, the adhesive can bedirectly activated and cured by the ultrasonic waves emitted by thepiezo element.

In a third variant of the invention, the adhesive layer is at least incertain regions producible from an adhesive, which contains at least onepolymerization activating component, which is activatable under theaction of microwaves. A corresponding component can be e.g. apolymerization initiator, which, however, is first activated forpolymerization by energetic microwave input. In a subvariant, apolymerization activating component can also be present in amicro-encapsulation, wherein the micro-capsule is destroyed by themicrowaves and the component, in this way, released and, thus,activated.

In a fourth variant of the invention, the adhesive layer is, at least incertain regions, enriched with a component, which is inductivelyheatable under the action of LF- or HF-fields. This can be, for example,ferromagnetic alloys or metals such as nickel-iron.

Advantageous embodiments of the invention are subject matter of thedependent claims.

The cured adhesive layer can have unreacted photo initiators or residualmonomers, with functional groups, which form chemical bonds or radicalsunder photochemical irradiation. The cured adhesive layer can preferablyhave residues of a micro-encapsulation. The cured adhesive layer canadditionally have residues of a component absorbing LF- or HF-fields.The adhesive layer can additionally have residues of a microwaveabsorbing component, such as e.g. ferromagnetic particles.

The metal disk can have an area facing the piezo element with ageometric center of gravity, wherein the degree of crosslinking of thepolymer decreases toward this center of gravity. This means, forexample, that the polymer on the edge of the adhesive layer is subjectedto an increased polymerization process as compared with the center. Thisform of a laterally increased degree of polymerization can be initiatedby lateral irradiation. This is explained in greater detail withreference to FIGS. 2-8.

For an exactly fitting orienting of the metal disk and of the piezoelement relative to the coupling body, it is, consequently, advantageousto perform a pre-affixing, or tacking, before the actual curing. Thepre-affixing enables a securement of the piezo element and the metaldisk with the coupling body.

The adhesive layer can be cross-linked in an edge region of the metaldisk photochemically or by microwave incidence and thermallycross-linked in a central region. This can be observed, for example, bynoting that photo initiator molecules are still unactivated in thecenter of the adhesive layer and not connected as components of apolymeric network, but, instead, are surrounded in increasedconcentration only by a polymeric material, without forming of chemicalbonds or at least no bonds activated by irradiation.

The coupling body, respectively the coupling element, can have acoupling surface facing the measured medium for the in- and/orout-coupling of an ultrasonic, wanted signal into and out of thecoupling element, and wherein the coupling element has at least onereflecting surface, which redirects radiation, especially UV radiationor microwave radiation entering from the coupling surface into thecoupling element into the edge region of the metal disk. In thisvariant, the reflecting surface is provided by the coupling element.Additionally or alternatively, also a reflecting coating can beprovided.

Additionally, a focusing of the radiation can occur on the reflectingsurface. The adhesive layer can especially be a 2-component adhesive,wherein at least one component is surrounded by the micro-encapsulation.Polymerization can occur after destruction of the micro-encapsulation.

The coupling body can advantageously be at least partially transparentand/or microwave transmissive. For example, upon irradiation of theadhesive from the coupling body toward the metal disk, curing of theadhesive occurs without additional measures.

The adhesive layer between the metal disk and the coupling body can havethe same chemical composition as the adhesive layer between the metaldisk and the piezo element.

An ultrasonic, flow measuring device of the invention for ascertainingthe flow velocity or the volume flow of a measured medium includes ameasuring tube and at least two ultrasonic transducers, as claimed inone of claims 1-4, arranged along the measuring tube, wherein each ofthe ultrasonic transducers has the coupling element with a couplingsurface, at which a produced ultrasonic signal can be transmitted orreceived into or out of the measuring tube or measured medium.

Also only one of the two adhesive layers can be provided in the regionof the metal disk. Thus, a λ/4-adapting, or matching, layer can also beprovided between the metal disk and the coupling element instead of theadhesive layer, as is described in detail in DE 10 2013 104 542 A1, towhich comprehensive reference is taken relative to this variant of theconstruction of an ultrasonic transducer. This concept is known to thoseskilled in the art. Of concern here is an adapting, or matching, layerhaving a layer thickness, which corresponds to a multiple of a fourth ofthe wavelength of the ultrasonic signal in the material of the adapting,or matching, layer, wherein the layer thickness can, depending onacoustic requirements at the bandwidth, also deviate by ±25% from thisvalue. This is in contrast to a typical adhesive layer, whose layerthickness lies at under ⅜ lambda.

BRIEF DESCRIPTION OF THE DRAWINGS

The subject matter of the invention will now be explained in greaterdetail based on a number of examples of embodiments in the appendeddrawing, the figures of which show as follows:

FIG. 1 is an exploded view of a first ultrasonic transducer of theinvention;

FIG. 2 is a sectional view of the first ultrasonic transducer;

FIG. 3 is a detail view of the ultrasonic transducer of the invention;

FIG. 4 is a detail view of a second ultrasonic transducer of theinvention;

FIG. 5 is a sectional view of a third ultrasonic transducer of theinvention;

FIG. 6 is a detail view of the third ultrasonic transducer of theinvention;

FIG. 7 is a detail view of a fourth ultrasonic transducer of theinvention; and

FIG. 8 is a detail view of a fifth ultrasonic transducer of theinvention.

DETAILED DISCUSSION IN CONJUNCTION WITH THE DRAWINGS

FIG. 1 shows an ultrasonic transducer 1 of the invention including acoupling element 3.

The ultrasonic transducer 1 comprises an arrangement of a piezo element2, a metal disk 4 and a coupling element 3. Arranged between the piezoelement 2 and the metal disk is a first adhesive layer 5. Arrangedbetween the metal disk 4 and the coupling element 3 is a second adhesivelayer 6.

Coupling element 3 is often also called a coupling body. Very often,coupling elements are embodied to have a wedge shape, so that thoseskilled in the art also speak of a coupling wedge.

In the present example of an embodiment, the coupling element 3 isembodied as a coupling wedge. The basic form of the coupling element iscylindrical with a lateral surface 3.1 and two main surfaces 3.2 and3.3. In such case, one of the two main surfaces 3.2 is tilted relativeto the other main surface 3.3, so that a normal vector X of the mainsurface 3.2 is at an angle to the normal vector Y of the main surface3.3. The normal vector X of the main surface 3.2 is, in such case, thesame as the normal vector at least of the piezo element 2 and/or themetal disk 4. Main surface 3.3 serves as coupling surface and leads anultrasonic, wanted signal in the case of a clamp-on ultrasonic, flowmeasuring device into the tube wall of a media conveying tube. In thecase of a so-called in-line flow measuring device, thus a device with afixedly installed measuring tube, the ultrasonic, wanted signal can alsobe introduced directly into the medium.

The coupling element 3 shown in FIG. 1 has a special cavity 7 in theform of an inclined bore, in which the piezo element 2 and the metaldisk 4 are securable.

Cavity 7 in the coupling element 3 in the present example of anembodiment is a cylindrical recess containing the circularly shaped,main surface 3.2. Depending on shape of the piezo element 2, however,also other geometric forms are conceivable. Thus, the main surface 3.2in cavity 7 can be square or rectangular, for example.

At the main surface 3.2, the greater part, thus greater than 50%, of theultrasonic signal produced by the piezo element is introduced into thecoupling element 3. At the same time, the angular deviation of the mainsurface 3.2 from a parallel orientation to the main surface 3.3 definesthe angle of incidence of the ultrasonic signal into the measuredmedium.

Introduced into the cavity is an adhesive for adherring the couplingelement 3 with the metal disk 4. This forms, after its curing, thesecond adhesive layer 6. The terminology, adhesive, in the sense of theinvention means any substance, which is curable and in this cured stateprovides an affixing between two elements, here the metal disk 4 and thecoupling element 3 or the metal disk 4 and the piezo element 2.

The adhesive layers have especially a thickness of up to a maximum of 1mm thick, preferably, however, a maximum of 0.5 mm thick. Alternatively,the bonding between the metal disk 4 and the coupling element 3 canoccur through use of a potting compound of thickness equaling a multipleof lambda/4.

Four variants of the invention can be used for forming the adhesivelayer. In each case, the object of a fast fixing of the individualcomponents at lesser temperature loading is solved in a differentmanner.

For forming the first and/or second adhesive layer 5, 6 according to afirst variant of the invention, a photochemically curable adhesive canbe utilized.

To the corresponding photochemical adhesives belong, among other things,the UV adhesives, which can be obtained e.g. from the the firm, Loctite.

One option is that a one-component or multi-component adhesive isactivated upon UV irradiation and forms bonds. This is the case, forexample, for photo initiated curing acrylates. Alternatively, also a socalled photo activator can be utilized, which is first of all activatedby exposure to UV-light, for example, with radical formation, and thenthese radicals excite other components of the adhesive for chainreaction/cross-linking.

Suitable fundamental systems for adhesive components are e.g. acrylates,polyurethanes or epoxide resins. The curing can be enabled, for example,using an LED curing lamp, e.g. a Delolux 80 lamp. The temperature rise,is, in such case, significantly less than with a conventional dischargelamp. The light wavelength is preferably in the range, 300 to 480 nm.

For forming the first and/or second adhesive layer 5, 6 according to asecond variant of the invention, an adhesive can be used, which containsat least one micro-encapsulated polymerization activating component,which is releasable under the action of microwaves.

Micro-encapsulations are known per se and are applied extensively e.g.in the foods industry. Also, micro-encapsulated adhesives are known perse (see “Kleben-Grundlagen, Technologien, Anwendungen (AdhesiveBonding—Fundamentals, Technologies, Applications)”; sixth updatededition, pages 238-240). Such adhesives are applied e.g. in the case ofthe adherring of screws, where the micro-capsules are destroyed by theshearing. Such adhering, thread pre-coats are used e.g. in products ofthe firm, PreLok. Micro encapsulations with enclosed adhesive componentsare producible, for example, by the so-called drop method. In such case,at least one component is present in the micro-encapsulation, for, ingiven cases, together with additional components, triggering a polymericchain reaction. Such component can be, for example, a hardener. In thecase of epoxides, the hardener can be, for example, a multiple amine(e.g. diethylenetriamine). Alternatively, also a component of theadhesive, e.g. a polyol, can be enclosed in the micro-encapsulation.

High energy microwave radiation enables a bursting of themicro-encapsulations. In this way, polymerization occurs and/orcross-linking of already existing polymer chains.

Additionally, the micro-encapsulation, the encapsulated componentsand/or the unencapsulated components can advantageously include otheringredients, which strongly heat up under microwave irradiation or byinduction and thereby pointwise develop heat, which supports thepolymerization- and/or cross-linking reaction. A greater external heatinput, which burdens the other components, e.g. the coupling body or thepiezo element, is, consequently, not necessary or at least onlynecessary to a lesser degree. These other ingredients are heat absorbingparticles, thus e.g. metal particles.

For forming the first and/or second adhesive layer 5, 6 according to athird variant of the invention, an adhesive can be used, which containsat least one micro-encapsulated polymerization activating component,which is releasable under the action of ultrasonic waves.

Such a technology is applied e.g. in the medical field, in order torelease ultrasonic, contrast means by way of ultrasonic action. Acorresponding technology and the micro-encapsulations are described inEP 0 977 594 B1, to which comprehensive reference is taken.

In contrast to the technology there, the micro-encapsulation in thepresent case is utilized for enclosing an adhesive component. Themicro-encapsulations can be made to burst by the ultrasonic waves of thepiezo element 2 of the ultrasonic transducer 1. In this way, thearrangement provided for measuring is also utilized for its manufacture.For this, the piezo element can be supplied with an excitation energyduring the manufacturing process, which is higher than the usualexcitation energy for the measuring mode.

Also, in the present case, the micro-encapsulation, the encapsulatedand/or the unencapsulated component can contain ingredients, whichstrongly heat up under microwave irradiation or by induction and therebyprovide pointwise hot spots, which support the polymerization- and/orcross-linking reaction. Also here, the heat absorbing particles can bee.g. metal particles.

For forming the first and/or second adhesive layer 5, 6 according to afourth variant of the invention, an adhesive can be utilized, which isenriched at least in certain regions with a component, which is heatableinductively under the action of LF- or HF-fields

Such components can be e.g. ferromagnetic alloys or metals, such asnickel-iron. These components are also detectable in the adhesive layerafter the curing. The adhesive layer contains, consequently, also in thecured state, residues of an LF- or HF-field absorbing component.

A special advantage of heating with microwaves, induction or also of themicro-encapsulation is the locally limited effect and, thus, apolymerization, which protects surrounding materials. In such case, theheat input for this polymerization is very small.

After started polymerization, the adhesive layer can be only pre-affixedor else completely cured in one process step. In the case of apre-affixing, a heat treatment can follow for bringing about a completepolymerization. In such case, the heat input can advantageously beselected smaller, so that also in this case, a heat protectingmanufacture for the residual components is possible (thus protectinge.g. the material of the piezo element or the material of the couplingelement).

Known concepts for securement of a bearing plate are designed to connectthe bearing plate immediately with the piezo element or the couplingbody. Application of the aforementioned adhesives permit a steppedcuring of the adhesive.

In the case of application of a photochemically curable adhesive andwith irradiation as shown in FIGS. 2 and 3, the irradiation e.g. withultrasonic waves and/or microwaves effects a lateral affixing of themetal disk 4 to the coupling element 3. This is understood as a type ofpre-affixing, or tacking. This lateral affixing respectively betweencoupling element and metal disk and between metal disk and piezo elementprotects these elements against slipping before a final curing occurs.

After transpired pre-affixing, depending on intensity of theirradiation, a fine adjustment, respectively fine orientation, of theindividual components of the ultrasonic transducer arrangement can stilloccur.

A final curing and therewith an affixing can occur, for example, rightafter the pre-affixing, in a furnace or alternatively by full surfaceirradiation of the coupling element 3, to the extent that couplingelement 3 is transparent relative to the polymerization promotingradiation, e.g. UV radiation.

In a third ultrasonic transducer arrangement of the invention, theapplied adhesive can contain a micro-encapsulated, polymerizationactivating component, which is releasable under the action of ultrasonicwaves.

A special advantage of this variant is that the ultrasonic waves of theultrasonic transducer can burst the micro-encapsulations. In a firstfrequency, which corresponds to the resonant frequency of themicro-capsules, thus, the capsules are caused to burst. Ultrasonic wavesare transmitted as measurement signals with a second frequency. A usercan determine a percentage of capsules it would like to burst as afunction of the duration of the frequency. Thus, it is possible topre-affix, to orient and, finally, to affix the metal disk.

The aforementioned securement methods hold preferably both for formingthe first as well as also the second adhesive layer.

The irradiation of the lateral regions of the metal disk, respectivelythe adhesive layers, for pre-affixing can be achieved by positioning aradiation source in this lateral region.

It is, however, also possible to embody the coupling element 3 in such amanner that a free space 8 is present between the edge of the metal disk4 and the edge of the piezo element and the inner surface of the cavity7. An ultrasonic transducer with such a coupling element 3 is shown inFIGS. 2 and 3.

The radiation S from the radiation source, thus e.g. from theultrasonic, microwave- or UV radiator, enters the free space 8 of thecoupling element 3 and travels straight to a redirecting surface 9,where the radiation is redirected a. The redirecting surface 9 can beprovided with a radiation reflecting layer or an ultrasonic wavereflecting layer. This occurs in FIG. 2 with an angle of 90°. In thisway, the radiation is directed parallel or essentially parallel to thefirst and/or second adhesive layer 5, 6 and enables an edge curing forpre-affixing the components, respectively the piezo element 2, the metaldisk 4 and the coupling element 3, on top of one another.

Then, a fine orientation of the metal disk or of the piezo element canoccur, or a transport step can occur within a manufacturing plant.

Finally, a curing can occur by irradiating centrally located adhesivethrough the coupling element or by thermally curing the adhesive. Insuch case, preferably a smaller energy can be expended than in the caseof a usual thermal cross-linking without previous photochemical curing.

FIG. 4 shows another advantageous variant, which can be used e.g. for aphotochemical curing, an ultrasonic wave- or a microwave activatedcuring. In such case, the coupling body includes a focusing surface 9.This can be milled into the coupling body and then coated with a layer,e.g. a metal layer, which turns and focuses incoming radiation orultrasonic waves in the direction of the adhesive layers 5, 6.

FIGS. 5 and 6 show a variant, in the case of which radiation orultrasonic waves passing through the coupling body 3 are reflected on aredirecting surface 10 laterally in the direction of the adhesive layers5 and 6. In this version, the redirecting surface is coated with areflecting layer, which provides a reflecting surface.

FIGS. 7 and 8 show respective variants of the focusing, whichsupplementally focus the incoming radiation or ultrasonic waves andthereby steer such with targeting onto the lateral region of theadhesive layer.

In FIG. 7, this occurs on a focusing surface 10, which is a reflectinglayer applied on the coupling element 3. The contour, respectivelybulge, of the focusing surface 10 can be integrally worked into thecoupling body 3.

In FIG. 8, the focusing occurs with the aid of a special focusingelement 11, which protrudes inwardly into the free space 8. Thisfocusing element 11 provides a focusing surface 10, on which the turningand focusing of radiation or ultrasonic waves occurs. Focusing element11 can be arranged releasably on the coupling element 3, so that it canbe reused in the production process.

Of course, a corresponding focusing element can also be arranged in FIG.4 in place of the focusing surface 9 there.

In an additional variant (not shown) of the invention, the adhesivelayer can be provided with energy conductors, thus e.g. light conductorsor sound conductors. These enable the energy- and/or radiation to beinput exactly to the position to be adhered.

1-15. (canceled)
 16. An ultrasonic transducer, comprising: a couplingelement; a metal disk; and a piezo element, wherein: between saidcoupling element and said piezo element said metal disk is arranged;said metal disk is connected with said piezo element or with saidcoupling element by means of an adhesive layer; and said adhesive layeris enriched, at least in certain regions, with a component, which isheatable inductively under the action of LF- or HF-fields.
 17. Theultrasonic transducer as claimed in claim 16, wherein: said adhesivelayer has residues of a micro-encapsulation or residues of an LF- orHF-field absorbing component or residues of a microwave absorbingcomponent.
 18. The ultrasonic transducer as claimed in claim 16,wherein: said metal plate has an area facing said piezo element with ageometric center of gravity; and the degree of crosslinking of thepolymer decreases toward this center of gravity.
 19. The ultrasonictransducer as claimed in claim 16, wherein: said coupling element has acoupling surface facing the measured medium for in- and/or out-couplingof an ultrasonic, wanted signal into and out of said coupling element;and said coupling element has at least one reflecting surface, whichredirects radiation, especially a UV radiation or microwave radiation,or ultrasonic waves, entering from said coupling surface into saidreflecting element and into the edge region of said metal disk.
 20. Theultrasonic transducer as claimed in claim 16, wherein: said couplingelement has a focusing surface for focusing radiation, especially UVradiation or microwaves, or ultrasonic waves, onto a lateral region ofthe adhesive.
 21. The ultrasonic transducer as claimed in claim 16,wherein: said adhesive layer is produced from a 2-component adhesive,wherein at least one component is surrounded by the micro-encapsulation.22. The ultrasonic transducer as claimed in claim 16, wherein: within acavity of said coupling element, in which cavity said piezo element andsaid metal disk are arranged, a focusing element and/or reflectionelement are/is arranged, for focusing and/or redirecting radiation,especially a UV radiation or microwave radiation, or ultrasonic waves.23. The ultrasonic transducer as claimed in claim 16, wherein: saidcoupling element is at least partially transparent and/or microwavetransmissive.
 24. The ultrasonic transducer as claimed in claim 16,wherein: said adhesive layer is arranged both between said piezo elementand said metal disk, as well as also between said metal disk and saidcoupling element; and said adhesive layer between said metal disk andsaid coupling element has preferably the same chemical composition asthe adhesive layer between said metal disk and said piezo element. 25.The ultrasonic, flow measuring device for ascertaining flow velocity orvolume flow of a measured medium, comprising: a measuring tube and atleast two ultrasonic transducers as claimed in claim 16, arranged alongthe measuring tube, wherein: each of the ultrasonic transducers has thecoupling body with a coupling surface, at which a produced ultrasonicsignal can be transmitted or received into or out of the measuring tubeor measured medium.